1. Field of the Invention
The present invention relates to a method of and an apparatus for removing non-metallic inclusions and intermetallic compounds from a molten metal.
2. Description of the Prior Art
It is known that non-metallic inclusions and intermetallic compounds (generally referred to as "inclusions", hereinafter) in a molten metal causes defects in the final product produced from the metal. Various studies have been therefore made to develop techniques which enable an efficient removal of such inclusions. For instance, Japanese Patent Laid-Open Publication Nos. 55-107743 and 58-22317 disclose methods in which horizontal rotational flow is imparted to a molten steel so that non-metallic inclusions are concentrated to the central region due to centrifugation. Japanese Patent Laid-Open Publication No. 63-219536 discloses a method in which drifting dross in a molten zinc bath is maintained at a predetermined temperature which provides a required level of fluidity of the bath during centrifugal separation.
These known methods rely solely upon mechanical separation such as centrifugation and cannot effectively separate fine particles, although they can efficiently separate comparatively large particles of non-metallic inclusions and impurities.
A method disclosed in Japanese Patent Laid-Open Publication No. 61-103654, relies solely upon heating of molten metal, but cannot produce appreciable effect in excluding large particles of non-metallic inclusions, in particular mixing of slag which is generated in unsteady state of a melt-forming proces, although this method is effective in preventing generation of non-metallic inclusions and removal of the small-sized non-metallic inclusions.